Here goes... (but still struggling with pics)
PIC 1.... This is the drive...
PIC 2.... The drive connects to the cog, which drives the toothed belt left over from my son's 3D printer build a few yrs ago...
PIC 3.... The Limit Switches
PIC 4.... The Serial Interface Board
PIC 5.... The Rotation Control Board
PIC 6 and 7.... The Auto Degaus Board
PIC 8.... The CRT And Surround (without the glass screen)
So, the basics...
At power ON, the timer relay on the rotate interface board (which is powered by the 12V from the ATX) will lockout the spurious outputs from the serial port for 30 seconds (this is adjustable).
When the PC boots and Mala is started it will be in the orientation of the last game played (thanks to Startcom). When V game is selected, Mrotate gives the output pulse on the Serial Port pin assigned. The interface board then powers a relay which activates the rotate system.
The rotate system, once activated, uses 2 relays to immediately block any further inputs, while at the same time activating 2 further relays. One will supply the drive voltage in the correct polarity and block out the other, or vise-versa, depending on direction of rotation. This state in permanent until the limit switch is hit. If a limit is not hit is the time set on the rotation timer relay the whole circuit is killed. This should hopefully never happen!!! When a limit is hit, a few things happen....
1. The rotation supply is disconnected and the rotation circuit resets ready for the next input.
2. The Motor Brake Relay is activated. This puts a resistor across the motor contacts for a couple of seconds to avoid over-run.
3. The Auto Degaus fires the appropriate PTC for 1 second.
There are 3 PTC fitted. One for auto c/w, one for auto anti c/w, and one for manual. As the auto PTCs are only fired for 1 second, and they are used alternately, and they are fan cooled, even if the rotate is operated at the fastest possible frequency, the PTC has cooled sufficient to be ready for use. Hopefully the manual PTC, fired from a switch behing the coin door, will never be needed.
Some more notes...
The rotate motor is only running on 12V even though it is a 24V motor. With the full 24V it draws around 8A on startup and runs far to fast. This will cause the relay contacts to fail and also cause over-run. At 12V the rotation is nice and smooth and controlled.
My machining capabilities are quite limited so the drive cog is not perfectly centered on the drive shaft. The CRT mounting disc, around which the toothed belt is fitted, is also not as perfectly round as I would have like. This combination of imperfections caused the drive mech to go tight / slack / tight / slack during operation, causing a very jerky rotation. I added the rather elaborate (and probably over engineered) tensioning rollers to get around this and the rotation is now nice and smooth.
Unfortunately I am a messy worker, and my circuit drawings were no more than scribbles with loads of alterations and scribbles and I struggled to understand them myself once I'd finished with them. If anybody does need this info I'll try to recreate them in a neat fashion. But, to be honest, I only went with all the relays (and timer relays) as they were what I had in my scrap box. My son thinks I am positively pre-historic, and said if he was doing this build he would have controlled everything via an Arduino with PWM motor drives, H Bridges, and other far more modern techniques. I admit that computers and Arduinos are far out of my area of competence.
I hope this info and the pics and videos are of use to some people out there, and will do another update when I have built the rest of the machine (mainly the hot-swap CPs) and loaded on loads more games. I'll also be asking more questions regarding Mame / Mala, as obviously I'll be wanting to hide all the DOS boxes that keep showing and make Mala auto start at boot, which I know are all possible.
I must say another massive THANK YOU to DaOld Man, without who's help this machine would have never got off the ground